Project Summary/Abstract Our investigation is directed at understanding how group 2 innate lymphoid cells (ILC2s) promote tissue regeneration. Innate and adaptive immunity converge during tissue trauma to play an instrumental role in regulating the balance between pro-inflammatory and anti-inflammatory responses that promote injury and regeneration, respectively. In previous studies examining the role of regulatory T cells (Tregs) in tissue regeneration, we used IL-2 complex (IL-2c) to increase Tregs during tissue degeneration, and found that IL-2c robustly increased Treg numbers, resolved tissue inflammation and reduced injury, indicating that Tregs aid in tissue regeneration by modulating the inflammatory response to injured tissue. Recent studies have reported that IL-2c also robustly increases ILC2s, and modulation of tissue inflammatory responses in response to IL-2c treatment were attributed to increases in ILC2s in a mouse model of type 1 diabetes. Based on these observations we will examine the role of ILC2s in tissue regeneration using skeletal muscle as a model system for out investigation. Skeletal muscle provides several advantage including 1) it is a highly regenerative tissue, 2) has a well-defined tissue stem cell niche, and 3) previous studies have shown that innate immunity is important for efficient muscle regeneration. The focus our study is centered at testing the hypothesis that ILC2s promote muscle regeneration through the modulation of type 2 innate inflammatory responses and direct interactions with muscle stem cells that regulate stem proliferation and/or differentiation. In preliminary work, we show that ILC2s are activated by tissue injury, IL-2c significantly increased ILC2s during muscle regeneration, and that IL-2c increases the size of muscle fibers, suggesting that ILC2 regulate muscle regeneration or growth. In specific aim 1, we will characterize the role of ILC2s in muscle regeneration, and examine their capacity to directly regulate the myogenic function of muscle stem cells (mSCs). We predict that ILC2-derived amphiregulin (Areg) directly acts on mSCs to modulate their proliferation and/or differentiation. In specific aim 2, we will examine the capacity of ILC2s to regulate sterile, type 2 innate immunity, which was previously shown to be critical for efficient tissue regeneration. We predict that ILC2s, through their production of IL-5 and IL-13, directly activate eosinophils (Eos) and M2 macrophages, innate immune cells that were both shown to promote muscle regeneration. Collectively, the proposed work promises to advance our understanding of the diverse biology of ILC2s by showing that ILC2s are critical immune cells that guide efficient tissue regeneration by regulating inflammatory responses that promote regeneration, and through direct interaction with tissue stems cells that a required for regeneration. Moreover, our study will reveal new therapeutic pathways that may be targeted to promote regeneration in a broad class of clinical settings, including acute trauma, degenerative disorders and autoimmunity resulting in destruction of tissues.